1. Field
The present embodiments relate to a magnetic detection device for detecting an external magnetic field by detecting a change of the resistance value of the device, and in particular, an object of the present invention is to provide a magnetic detection device having highly accurate magnetic detection by adjusting the resistance value.
2. Description of the Related Art
Usually, to detect a change of an external environment by using a variable resistance element whose resistance value is changed by the external environment, the variable resistance element is connected in series to a reference resistance element whose resistance value does not change, and the thus serially connected variable resistance element and reference resistance element are subjected to a direct current voltage. Then, a midpoint potential between the variable resistance element and the reference resistance element is detected. Thereby, the change of the resistance value of the variable resistance element can be accurately detected without being affected by the environmental temperature.
In this type of magnetic detection device, it is necessary to adjust the midpoint potential between the variable resistance element and the reference resistance element by adjusting the resistance value of the reference resistance element. The midpoint potential is preferably set to be one half the value of a power supply voltage.
As described in Japanese Unexamined Patent Application Publication Nos. 2001-35702 and 2001-44001, a conventional method of adjusting the resistance value is performed by forming a resistance element on a substrate and thereafter removing a part of the resistance element through trimming.
In the resistance value adjusting method described in the above publications, resistive films formed into square frames are partially removed. However, the resistive films positioned on the respective sides of each of the squares all have the same resistance value. Thus, when any one of the resistive films is trimmed, the amount of change of the overall resistance value is small. It is therefore difficult to obtain a wide adjustment range of the resistance value.
Further, to obtain the wide adjustment range of the resistance value, it is necessary to provide a large number of the square frames formed by the resistive films, as described in Japanese Unexamined Patent Application Publication No. 2001-44001. Furthermore, to trim the resistive films, it is necessary to calculate the positions of the resistive films to be removed by using a complicated formula. As a result, the structure of the resistive films for adjusting the resistance value becomes complicated, and the adjustment operation of the resistance value also becomes complicated.